Changes in matter

chemists classify matter in two different states chemical and physical.

matter: anything that has mass and occupies space. matter can be organized into pure substances and mixtures.

pure substance: cannot be broken down into simpler substances.grouped into elements or compounds.

element: substances composed of only one kind of atom. ie. hydrogen, oxygen, and gold.

compound: substances composed of two or more elements chemically combined. i.e. water, and sugar.

mixture: can be separated into component parts by physical means.

Physical changes: a substance changes in form but not in chemical composition. i.e. ice melting

chemical change: causes one or more new substances to be formed, may be difficult or imposable to reverse ie. burning paper.

if you have made more than two observations then a chemical change has probably occurred. heat is produced or absorbed. the starting material is used up. there is a change in color. a material with new properties is formed. gas bubbles form in a liquid. a precipitate forms in a liquid. the change is difficult to reverse.

chemists classify properties to gain a better understanding about matter.

matter can be identified by physical and chemical properties. physical properties are easily observable and include characteristics such as melting point, density, color, and state. density: amount of matter that occupies a certain space; the mass per unit volume of a substance. physical properties are further classified as qualitative or quantitative. qualitative: can be described, but might not be measured. quantitative: a quantitative can be numerically measured.

chemical properties refer to how the substance reacts to other substances. ei. iron is a reddish solid (physical properties) that reacts with oxygen to form rust (chemical properties) combustibility: is the ability of a substance to burn in oxygen it is not a physical property because combustion creates new substances.

what are elements
Lavoisier law of conservation of mass in a chemical change the total mass of the new substance is always the same as the total mass of the original substance. the law of definite composition compounds are pure substances that contain two or more elements combined together in fixed (or definite) proportions.

voltaic pile: is a device we now call a battery. it wasn't as efficient as our batteries today, but delivered a reliable supply of electricity to pass through water.

electrolysis: the process of decomposing a chemical compound by passing an electrical current through it.

daltons atomic theory

all matter is made up of small particles called atoms. atoms cannot be crated, destroyed, or divided into smaller particles. all atoms of the same element are identical in mass and size. atoms of one element are different in mass and size from the atoms of other elements. compounds are created when atoms of different elements link together in definite proportions.

classifying elements

the first chemist to report a new element got the right to name it.

element symbols: the system of element symbols provided symbols for all the known elements it also showed how to create symbols for any new elements that might be discovered.

one of the ways of classifying elements is in metals, non-metals, and metalloids. state at room temperature appearance conductivity malleability and ductility metals solids, except for mercury shiny luster good conductors of heat and electricity malleable ductile non-metals some gasses some solids only bromine is a liquid not very shiny poor conductors of heat and electricity brittle ductile metalloids solid can be shiny or dull may conduct electricity poor conductors of heat brittle non ductile chemical families: a group of related elements that have similar properties.

alkali metals are so reactive they need to be specially stored.